5.1.1 Nested browsing contexts

Certain elements (for example, iframe elements) can instantiate further browsing contexts. These are called nested browsing contexts. If a browsing context P has a Documents D with an element E that nests another browsing context C inside it, then C is said to be nested throughD, and E is said to be the browsing context container of
C. If the browsing context container element E is in the DocumentD, then P is said to be the parent browsing context of C and C is said to be a child browsing context of P. Otherwise, the nested browsing contextC has no parent browsing context.

5.1.2 Auxiliary browsing contexts

It is possible to create new browsing contexts that are related to a top-level browsing context without being nested through an element. Such browsing contexts are called auxiliary browsing contexts. Auxiliary browsing contexts are always top-level browsing contexts.

5.2.1 APIs for creating and navigating browsing contexts by name

Opens a window to show url (defaults to about:blank), and returns it. The target argument gives the name of the new window. If a window exists with that name already, it is reused. The replace attribute, if true, means that whatever page is currently open in that window will be removed from the window's session history. The features argument is ignored.